The power of portable communications devices such as Pocket PCs, PDAs and tablet PCs, together with the emergence of wireless local area networks (LANs), is viewed as an attractive combination by organizations seeking to create a highly mobile extension of the corporate LAN. In one scenario, users can place telephone calls to each other over the packet-based network rather than utilize dedicated circuits in the public-switched telephone network (PSTN). When the packets are Internet Protocol (IP) packets, this technique is known as “voice over IP”, or VoIP for short. In VoIP, analog speech signals received from an analog speech audio source, for example a microphone, are digitized, compressed and translated into IP packets for transmission over the wireless LAN.
Corporations have generally recognized that the deployment of VoIP allows a more efficient use of their telecommunications infrastructure and, in the case of long distance calls, can be used to bypass the toll structure imposed by the service providers that operate the PSTN. However, an underlying security problem exists when a VoIP application is implemented in mobile communications devices. Specifically, the wireless operating mode of these devices makes them vulnerable to “air gap” attacks which can lead to unauthorized eavesdropping of voice conversations, for example.
Similar security problems arise in other VoIP applications which lie outside the wireless realm. In particular, home PCs that connect to an Internet service provider (ISP) via a residential telephone (POTS) line can implement a VoIP application. In such an environment, the home PC provides the digitizing, compression and translation functions. In this case, the existence of a connection to the Internet via the ISP can be viewed as an alternative to joining two endpoint communication devices that ordinarily would connect through the PSTN. However, as the Internet is basically a collection of routers belonging to different entities, each such router represents a point of vulnerability, providing easy and undetectable replication of the data for malicious or illegal purposes.
Yet another scenario where a security breach may occur is in the case of a POTS-to-POTS call, where at least part of the call traverses a packet-switched network. Gateways are positioned at the entry and exit points of the packet-switched network, providing POTS-to-IP and IP-to-POTS conversion. Such an arrangement is increasingly likely to take place as carriers head towards voice/data convergence and utilize their packet-switched networks more effectively. However, under this scenario, the IP packets used to transport the call through the packet-switched network are exposed to detection and replication at the gateways, as well as at each router traversed within the packet-switched network.
It will be appreciated that the common denominator to each of the above security breach scenarios is the vulnerability of IP packets as they transit a packet-switched network. Whereas access to a connection that transits only the PSTN between the two end points of a call requires the line to be physically “tapped”, the existence of a packet-switched network along the communications path provides a means for eavesdroppers to access the data being transmitted without detectably disturbing the connection, allowing the data so obtained to be collected, stored, analyzed, retransmitted, etc. without either party's authorization or even knowledge.
Accordingly, the focus has shifted to providing security for VoIP calls. One approach to increasing the security of a VoIP call has been the use of encryption. Specifically, in the case of two VoIP devices responsible for digitizing and packetizing the analog signal received from the user at either end of a call, it is possible to design the VoIP devices to provide encryption and decryption functionality, which make it difficult to decipher the underlying data without knowledge of a special key. While it may be appropriate to implement this solution as an added feature of new VoIP devices, it does not solve the problem of a legacy device, such as a first-generation VoIP device or a standard POTS phone, wishing to participate in a VoIP call that is required to be secure while it potentially traverses a packet-switched network.
Clearly, therefore, a need exists in the industry to allow legacy devices, including POTS phones and first-generation VoIP phone, to establish secure VoIP communications with a called party endpoint.